As an analysis method (TDLAS: Tunable Diode Laser Absorption Spectroscopy) adapted to sweep an oscillation wavelength by modulating the injection current of a semiconductor laser, and obtain the absorption spectrum of measurement target gas to quantify concentration, a wavelength modulation method (WMS: Wavelength Modulation Spectroscopy) adapted to apply current modulation having small amplitude at a frequency sufficiently higher than a frequency used to modulate the current for the wavelength sweeping, and obtain the spectrum from a signal lock-in detected at a frequency twice the sufficiently higher frequency to quantify the concentration is often used in order to increase detection sensitivity.
For example, Patent Literature 1 discloses an example of a laser gas analyzer based on the wavelength modulation method (or also referred to as a frequency modulation method). In this example, the need for a reference gas cell for scanning the absorption wavelength of measurement target gas, i.e., for scanning the emission wavelength of a laser element is eliminated, and without stabilizing the emission wavelength to a specific wavelength, or without separately using a meter such as a dust meter even in a dusty environment, gas concentration can be accurately measured by correcting the amplitude of a gas absorption waveform using a received light amount correction coefficient.